Regulating Locomotion of Hydrogel Using Light and Electric Fields Holds Key in Developing Autonomous Materials

Hydrogel is a material known for having high absorbency and holding large amounts of water. They are currently used in various applications, such as tissue engineering, drug delivery, and biosensors. Recently, scientists have explored using hydrogels for locomotion since they can play an important role in soft robotics and biomedical devices.

Potential of Autonomous Materials

Conventional robots are typically designed to accomplish simple tasks such as gripping, lifting, swimming, or walking. In most cases, each motion can only be performed under direct human control or pre-programmed instruction.

Although there are self-propelled catalytic particles and light-powered micromotors, programmed stimuli are still needed to combine a series of locomotions into more complex functions. Such robotic systems require external control units and human supervision and cannot accomplish complex tasks that involve a sequence of varying steps on their own.

Soft materials with autonomous functionality offer promising applications as smart, robotic tools in complex, dynamic environments. Soft robots can perform tasks deemed dangerous for humans, like navigating through tight spaces or hazardous environments. In medicine, they can be an important part of drug delivery systems or sensors that can navigate the body to identify and treat diseases.

They are not only beneficial in human-machine interfaces but in biomedical devices as well. Developing this material requires a functional soft matter that can effectively complete a well-organized task without step-by-step control.

Controlling the Movement of Hydrogels

In materials science, experts aim to develop autonomous materials that can perform various tasks beyond stimulus-responsive actuation. However, mimicking the high-level complexity and intelligence of biological actuators in artificial systems remains challenging. To attain the autonomous functionalities of soft robotic tools in complicated and unstructured environments, pairing multiple stimuli and designing for responses to environmental changes is necessary.

In the Center for Bioinspired Energy Science at Northwestern University, a research team developed hydrogels activated with light and electric fields for cargo capture and delivery. Led by Yang Yang, the researchers enabled photo-regulated charge reversal and autonomous functions under a constant electric field. They also used perturbations in the electric field induced by dielectric inhomogeneity.

In this study, spiropyran moieties with varying substituents were covalently integrated by Yang and his colleagues—finite element simulationsguidedg the design and movement of the charged hydrogels. Additionally, 3D surface profiles were engineered for maximized dielectrophoretic effect.

Two different spiropyran molecules with different net charges were used by the researchers. The team synthesized each of the molecules using a polymerizable methacrylate group. After the hydrogels have been electroactivated, they are photoregulated based on the charge reversal properties of the polymers.

The study examines the scope of electroactive movement and photoactuation in the spiropyran hydrogels. The analysis reveals that the photo- and electro-activated hydrogel can capture and deliver cargo and avoid obstacles. It can also return to its point of departure based on the constant delivery of visible light and applied electricity. Such conditions provided the energy needed to guide the hydrogel.

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